Selective Laser Melting (SLM)

Question 1

What is and what are the main features of selective laser melting (SLM)?

Answer 1

• high power laser is used to to directly melt the high Tmelt powder resulting in a phase change
• An inert environment is essential to prevent oxidation
• Parts are built on a thick substrate to overcome thermal stresses

Question 2

What are the 6 typical system paramemters for SLM?

Answer 2

Laser power - 200-1000 watts
Inert atmosphere - argon
Build volume - 250x250x250 mm
Powder diameter - 45 µm
Layer thickness - 25-60 µm
Minimum feature size - 250 µm

Question 3

What are the 8 stages of the SLM process?

Answer 3

1. Install build plate and inert atmosphere
2. Drop piston by one layer thickness
3. Activate the dosing system
4. Deposit powder across the build area
5. Scan the laser system to metal the powder in the desired pattern
6. repeat steps 2-5 until componant is complete
7. Lift the build piston to the starting position and remove excess powder.
8. Remove completed componant

Question 4

What are the requirements for Fibre lasers for SLM?

Answer 4

• laser unit contained in a standard, 19-inch rack
• lasers have no moving parts
• lasers have long life
• very stable power outputs and beam parameters
• Fibre laser wavelength is 1070nm (Ytterbium)
• Higher absorption into metals than CO_2 lasers

Question 5

What are the requirements for Fine powders and atmosphere for SLM?

Answer 5

• Small diameter (10-50 µm) must be used
• Small diameters makes powders explosive (particularly Ti, Al and Mg)
• Usually most of the powder can be recycled
• powder price up to £1000 per kg
• Atmosphere: Process gas reciruclated through the chamber and has high impact on material produced.

Question 6

What are the requirements for condensate control for SLM?

Answer 6

• Process gas must be re-circulated otherwise too much is consumed
• Must be filtered to remove condensed material
• must be handled with care (it’s very combustable)

Question 7

Briefly discuss reasons why the energy per unit mass/volume needed in practice in SLM may be
different to the theoretical case?

Answer 7

1. Heat losses
2. Non-uniform energy distribution
3. surface roughness
4. Ambient temperature changes throughout process.